Morphology: Obligate intracellular bacterium; biphasic life cycle (elementary body → reticulate body). No peptidoglycan — β-lactams inactive. Serovars D–K cause urogenital infection; L1–L3 cause LGV; A–C cause trachoma.
Typical drugs
- #1Doxycycline— 100 mg PO BID × 7 days — preferred by CDC 2021. Superior to single-dose azithromycin (~98% vs 94% cure for urogenital; significantly better for rectal infection).
- #2Azithromycin— 1 g PO × 1 — single-dose alternative when adherence concern. **Pregnancy first-line.** Adequate for urogenital but inferior for rectal CT.
- #3Levofloxacin— 500 mg PO daily × 7 days — alternative when neither doxy nor azithro tolerated.
Empiric therapy when resistant
Clinically significant resistance is rare. If treatment failure suspected, evaluate for re-exposure or M. genitalium co-infection (much higher azithromycin resistance).
Resistance notes
β-lactams intrinsically inactive (no peptidoglycan). Sulfonamides inactive. Aminoglycosides inactive.
Common syndromes
Pearls
Most common reportable STI in the US. Often co-tested with GC (urine NAAT for both). Asymptomatic in ~70% of women + 50% of men — screening is essential (annual in sexually active women ≤25, MSM, pregnant). Treat partners (expedited partner therapy where legal). Test-of-cure NOT routinely needed, but rescreen at 3 months for reinfection (high recurrence). Pregnancy: treat empirically if positive; do test-of-cure 4 wks after treatment. LGV (serovars L1–L3) — increasingly seen in MSM with proctocolitis; needs 21 days of doxycycline (not 7).
References
- CDC STI Treatment Guidelines (2021)
- USPSTF Chlamydia + Gonorrhea Screening (2021)